Microstructure development and defect formation during welding of aluminum alloys

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Welding processes, such as arc-welding and laser beam welding are increasingly being used to join aluminum alloys in the automotive and aerospace industries due to the potential of increasing process accuracy while reducing manufacturing costs. Although the use of these processes can result in improved material properties along with direct weight savings, certain inherent characteristics such as solidification cracking, microporosity, and heat-affected zone degradation must also be considered. The presence of these defects, even in small quantities, generally results in rejection of the welded part. The objective of the proposed research is to improve the quality and productivity of welding processes for aluminum alloy applications by reducing defect formation and improving the as-welded material properties. This objective will be realized through discovery of new fundamental knowledge relating welding solidification kinetics, alloy composition, and microstructure / defect nucleation and growth. Solidification experiments and semi-solid tensile tests will be performed to characterize the material's behaviour during welding. Computer simulations at the meso- and macro- scales will be developed in order to predict microstructure and defect formation along with the evolution in temperature and stress/strain in the fusion and heat-affected-zones. The results of the experiments and meso-scale simulations will be incorporated into the macro-scale model in order to link phenomena from different length-scales. This combination of experimentation and multi-scale modelling will enable assessment of the combined effects of welding parameters, alloy composition and microstructure variations on defect formation in order to optimize welding processes. Such optimization is critical for developing new innovative uses of aluminum alloys in passenger and mass transit vehicles.